Eta Cephei
Encyclopedia
Eta Cephei is a class K0
third-magnitude giant star
in the constellation
Cepheus
. Eta Cephei is an orange giant star with a very high proper motion
on the celestial sphere
. It is about 45 light-year
s from Earth
. Shared with θ Cep
, these stars have the title Al Kidr, meaning unknown
This star, along with α Cep
(Alderamin) and β Cep
(Alfirk), were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg.
In Chinese
, , meaning Celestial Hook
, refers to an asterism consisting of η Cephei, 4 Cephei, HD 194298, θ Cephei
, α Cephei
, ξ Cephei
, 26 Cephei, ι Cephei
and ο Cephei
. Consequently, η Cephei itself is known as .
According to Nelson & Angel (1998), Eta Cephei would show two significant periodicities of 164 days and 10 years respectively, hinting at the possible presence of one or more jovian planets in orbit around the subgiant. The authors have set an upper limit of 0.64 Jupiter masses for the putative inner planet and 1.2 Jupiter masses for the putative outer one. Also Campbell et al. (1988) inferred the existence of planetary objects or even brown dwarfs less massive than 16.3 Jupiter masses.
However, more recent studies have not yet confirmed the existence of any substellar companion around Eta Cephei. McDonald Observatory
team has set limits to the presence of one or more planets with masses between 0.13 and 2.4 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
third-magnitude giant star
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Cepheus
Cepheus (constellation)
Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...
. Eta Cephei is an orange giant star with a very high proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
on the celestial sphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...
. It is about 45 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Shared with θ Cep
Theta Cephei
Theta Cephei is a Class A7, fourth-magnitude star in the constellation Cepheus. Theta Cephei is a white spectroscopic binary star, located about 135 light-years from Earth...
, these stars have the title Al Kidr, meaning unknown
This star, along with α Cep
Alpha Cephei
Alpha Cephei is a second magnitude star in the constellation of Cepheus that is relatively close to Earth at only 49 light years...
(Alderamin) and β Cep
Beta Cephei
Beta Cephei is a third magnitude star in the constellation Cepheus. It has the traditional name Alfirk , meaning "The Flock" This star, along with α Cep and η Cep , were Al Kawākib al Firḳ , meaning "the Stars of The Flock" by Ulug Beg...
(Alfirk), were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg.
In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...
, , meaning Celestial Hook
Rooftop (Chinese constellation)
The Rooftop mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the northern mansions of the Black Tortoise.- Asterisms :...
, refers to an asterism consisting of η Cephei, 4 Cephei, HD 194298, θ Cephei
Theta Cephei
Theta Cephei is a Class A7, fourth-magnitude star in the constellation Cepheus. Theta Cephei is a white spectroscopic binary star, located about 135 light-years from Earth...
, α Cephei
Alpha Cephei
Alpha Cephei is a second magnitude star in the constellation of Cepheus that is relatively close to Earth at only 49 light years...
, ξ Cephei
Xi Cephei
Xi Cephei is a star in the constellation Cepheus. It has the traditional name Kurhah or Alkirdah or Al Kirduh, and the name was from Al Ḳurḥaḥ , an Arabic word that translated as a white spot, or blaze, in the face of a horse and other suggestion was Al Ḳirdah , the Ape.Xi Cephei belongs to...
, 26 Cephei, ι Cephei
Iota Cephei
Iota Cephei is a Class K0, third-magnitude star in the constellation Cepheus. Iota Cephei is an orange giant star located about 115 light-years from Earth. Due to precession of the equinoxes, it will become the pole star some time around 5200 CE.-External links:...
and ο Cephei
Omicron Cephei
Omicron Cephei is a binary star in the constellation of Cepheus. It consists of a less massive K-type main sequence star in orbit with a more massive G-type giant star. The overall apparent visual magnitude of the system is 4.75.The pair was first determined to be binary by F. G. W. Struve...
. Consequently, η Cephei itself is known as .
Hunt for substellar objects
According to Nelson & Angel (1998), Eta Cephei would show two significant periodicities of 164 days and 10 years respectively, hinting at the possible presence of one or more jovian planets in orbit around the subgiant. The authors have set an upper limit of 0.64 Jupiter masses for the putative inner planet and 1.2 Jupiter masses for the putative outer one. Also Campbell et al. (1988) inferred the existence of planetary objects or even brown dwarfs less massive than 16.3 Jupiter masses.
However, more recent studies have not yet confirmed the existence of any substellar companion around Eta Cephei. McDonald Observatory
McDonald Observatory
The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas...
team has set limits to the presence of one or more planets with masses between 0.13 and 2.4 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.